The present application relates generally to drilling tools used in the drilling of oil and gas wells, or similar earth drilling operations, and in particular to disconnection of a threaded rock drill bit from a threaded drill string member.
Background: Drilling
Oil wells and gas wells are drilled by a process of rotary drilling. In a conventional drill rig, as seen in FIG. 5, a drill bit 50 is mounted on the end of a drill string 52. As drilling progresses, more sections of collar and pipe are screwed onto the drill string, which may be several miles long. Surface equipment 51 includes a rotary drive (rotary table or top drive) which turns the string, including the bit at the bottom of the hole, and powerful pumps which pump drilling fluid (or "mud") through the string. The elements of the drill string are connected together by large screw threads.
Roller-Cone and Fixed-Cutter Bits
In contemporary drilling practice, there are two basic categories of rock drill bits: roller-cone bits and fixed cutter bits. Within each of these classifications, a range of sizes and design configurations are available.
A general schematic of a conventional rotary cone bit is shown in FIG. 3B. The most common roller cone bits have three independently rotating "cones" 336 (which may or be not be precisely conical) fitted on three bearings. The cones will have cutting elements 335 or "teeth" attached to, or integral with the cones. The bearings are mounted on "arms" 333 whose other ends are attached to a body 331. There is a threaded drill string connection 334 on the junction of the arms at the upper end of the bit. A further example of this type of rock drill bit is disclosed in U.S. Pat. No. 5,644,956 by Blackman.
A general schematic of a conventional fixed cutter bit 230 is shown in FIG. 2B. The most common fixed cutter bits have at one end a supporting structure referred to as the "bit head" 356. Wear-resistant cutting elements 231 are strategically located on the outer and lower surfaces of the bit head. Slot 240 and an identical slot on the far side of the shank 235 of the bit are explained in conjunction with the bit breaker with which it is used. A further example of this type of rock drill bit is disclosed in U.S. Pat. No. 5,033,559 by Fischer.
Drill bits will need to be replaced for a number of reasons. The most common reason for changing a drill bit is that it wears out and stops drilling. Another reason for changing a drill bit is to utilize a drill bit specifically designed for drilling a formation with the physical properties being drilled or one designed to provide certain performance characteristics, such as directional drilling. Another reason is to utilize a drill bit sized to produce the desired well bore diameter. To achieve the desired drilling and performance characteristics, a wide variety of drill bit designs are available.
Makeup and Breakout
As noted, the elements of the drill string are connected together by heavy threads. When a drill bit wears out or needs to be replaced for other reasons, the drill bit must be removed from the drill string. The torque required for this can be very substantial; for example, for a 26-inch bit, the specified makeup torque can be more than 40,000 pound-feet. (By comparison, the lug nuts on a typical light truck wheel require less than 100 pound-feet or torque.) These very large values of torque are needed to assure that the joint is not only mechanically stable under the high applied forces seen while drilling, but also sealed tightly against the high pressures of mud flow. Once a mud leak begins, the fine abrasive particles entrained in the mud can cause rapid erosion along the leakage channel.
For most of the joints in the string, the piece below the joint can be held by "slips" which support the drill string, while the piece above the joint is turned by mechanical pipe tongs. However, this is more difficult when attaching the drill bit itself, since the drill bit cannot be held by the slips which hold drill pipe or collar.
To keep the drill bit from turning when torque is applied to the joint, a "bit breaker" plate is used. FIG. 2A shows a bit breaker 200 used for fixed-cutter bits (such as shown in FIG. 2B). Bit breaker 200 has a base 210 and two arms 205, which mate with twin milled slots 240 on the shank 235 of the bit 230 to keep the bit from turning in relationship to the bit breaker. A latch 220 is normally included on the bit breaker plates, but this latch does not itself bear on the bit at all. In practice, this latch is often detached and discarded as soon as such a bit breaker plate is first used on the rig floor.
Fixed-cutter bits normally include a shank portion, into which the slots for a breaker tool are milled. Roller cone bits, however, normally do NOT normally include any such extended shank. There are several reasons for this, one of which is the undesirability of loss of mud pressure during passage through the interior of the bit. Another is the high rigidity required of the arm structures (since any bending in service can destroy the bit).
For roller-cone bits, a conventional bit breaker (as shown in FIG. 3A) simply has a cutout in its middle, into which the bit (shown in FIG. 3B) is lowered. The irregularities in this cutout engage the arms of the roller-cone bit, as shown in FIG. 3C.
The bit breaker plate fits into the rotary table. The internal geometry of the bit breaker is shaped so as to engage the bit securely and transmit torque from the rotary table to the drill bit in either right-hand or left-hand rotation. If the rotary table is held fixed, the bit will also be held fixed.
Correct operation of the bit breaker is important during make-up as well as during break-out. Any defect in assembly may lurk undiscovered until the bit is at the bottom of the hole, necessitating an extra trip to replace the bit. Any unexpected trip is extremely undesirable.
The process of "tripping" is required to change the bit. A heavy hoist pulls the entire drill string out of the hole, in stages of (for example) about ninety feet at a time. After each stage of lifting, one "stand" of pipe is unscrewed and laid aside for reassembly (while the weight of the drill string is temporarily supported by another mechanism). Since the total weight of the drill string may be hundreds of tons, and the length of the drill string may be tens of thousands of feet, this is not a trivial job. One trip can require tens of hours and add significant expense in the drilling budget. To resume drilling the entire process must be reversed.
Disadvantages of Available Designs
The standard bit breaker for a three cone bit has a bottom plate, four vertical side plates, and a top plate with an opening configured to engage the drill bit arms above the cones. One disadvantage of this design is that the bit breakers contact the drill bit arms at the lowest possible position, creating the possibility that the arms may be bent during the make-up of the tool joint, which destroys the drill bit. Another disadvantage of this design is that the bit breakers do not always accommodate the different cutting structures of the various design configurations, which can result in breakage of the cutting structure during the make-up of the tool joint. Another disadvantage of this design is that the bit breakers do not always accommodate extended nozzle designs, which can result in breakage or deformation of the nozzle during the make-up of the tool joint. Another disadvantage of this design is that the bit breakers are very heavy, making them physically hazardous and inconvenient to move. Another disadvantage of this design is that manufacturing costs are high as a result of the amount of material, machining, and welding required to build them. Another disadvantage of this design is that the bit breakers are large and bulky, requiring substantial storage space for each tool. Another disadvantage of this design is that it cannot be used to on fixed cutter bits.
The standard bit breaker for a fixed cutter bit is a U-shaped steel plate having a slotted opening sized for sliding engagement with the two parallel slots machined into the shank. These designs often include a safety bar to prevent the bit breaker from sliding off of the drill bit. One disadvantage of this design is that the open end of the tool reduces the tool's resistance to deformation, and widening. Another disadvantage of this design is that the safety bars are often discarded, making the tool more hazardous to use. Another disadvantage of this design is that it cannot be used on roller cone bits.
Since fixed cutter bits use different bit breakers than roller cone bits, a separate bit breaker is needed for every size in each design type. The total cost of manufacturing and inventorying the required number of bit breakers is substantial.
To address these problems, engineers have attempted to design bit breakers that can accommodate a wider range of drill bit sizes. In U.S. Pat. No. 4,495,840, Freitag and Smith disclose a bit breaker having a bottom engageable with the bottom of the bit, a top opening for lowering the bit into the bit breaker, and a pair of slidably mounted stop members for movement inward and outward relative to the opening. This design accommodates extended nozzle designs, and may accommodate drill bits of the next size tool joint. This design fails to accommodate fixed cutter bits, which now account for more than half of the total footage drilled worldwide. Another disadvantage of this design is that it requires a number of machined parts, which increases the manufacturing cost and reduces the reliability of the tool. Another disadvantage of this design is that it is bigger and heavier than conventional bit breakers.
Drill Bit And Make-Up/Break-Out Tool
In the preferred embodiment of the present disclosure, a generally square base has one open end, giving it a u-shape. The base is made of steel or other suitable material and is externally sized for placement in the rotary table of a drilling rig. A gate is pivotally attached at to one end of the open side of the base. A detachable connector such as a dowel pin secures the other end of the gate to the opposite open end of the base.
The base has a centered chuck-opening portion that is shaped to accommodate the cross-section of a roller cone drill bit. Two chocks integral to the base extend into the chuck opening. A third chock integral to the gate also extends into the chuck opening. When the gate is positioned adjacent to the open-end of the base, the three chocks form a symmetrical configuration of protrusions that align with the alternating recesses and protrusions found in the cross-section of a roller cone bit. Thus, when the tool is placed on a roller cone drill bit, the alignment of the chocks between the arms of the drill bit prevent rotation of the drill bit in either direction relative to the tool. Retaining slots formed between the arms of the roller cone bit engage the chocks to fix the vertical position of the bit breaker in relation to the drill bit. Similarly, a series of three equally spaced retaining slots are formed into the shank portion of the fixed cutter bit. The retaining slots engage the chocks to prevent rotation or movement of the drill bit in any direction relative to the tool, and to fix the vertical position of the bit breaker in relation to the drill bit. In this embodiment, the chucking system provides a bit breaker that is adapted for use on both roller cone bits and fixed cutter bits, and which is capable of performing without the many disadvantages of conventional bit breakers.
A significant advantage of the present disclosure is that it is the first bit breaker ever designed to be used for both fixed cutter bits or roller cone bits.
Another advantage of various disclosed embodiments is that roller cone bits are engaged closer to the tool joint, thus reducing the possibility of bending the arms of the drill bit during the make-up of the connection. PA1 Another advantage of various disclosed embodiments is that no contact with the bit's cutting structure occurs, thereby accommodating any cutting structure design safely. PA1 Another advantage of various disclosed embodiments is compatibility with extended nozzles on roller cone bits. (Extended nozzles can be useful for optimal control of fluid flow, but can be damaged by some conventional bit breakers.) PA1 Another advantage of various disclosed embodiments is lower cost than conventional bit breakers as a result of savings in the material, machining, and welding. PA1 Another advantage of various disclosed embodiments is bit breakers with reduced size and weight. This provides a reduced risk of injury on the job. PA1 Another advantage of various disclosed embodiments is less likelihood of deformation and widening of the bit breaker (as compared to a conventional fixed-cutter breaker) during the breakout operation.
Other advantages of the present disclosure will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the disclosed inventions are disclosed.